In Rust 1.55, you can read a file using the standard library's fs module and the File struct. There are a few different ways to read a file, depending on your needs. Here are some examples:
1. Reading the entire contents of a file into a string:
use std::fs;
fn main() -> std::io::Result<()> {
let contents = fs::read_to_string("file.txt")?;
println!("{}", contents);
Ok(())
}
This code reads the contents of the file "file.txt" into a string named contents, and then prints the string to the console. The read_to_string function returns a Result object, which we are handling using the ? operator to propagate any errors.
2. Reading the contents of a file line by line:
use std::fs::File;
use std::io::{BufRead, BufReader};
fn main() -> std::io::Result<()> {
let file = File::open("file.txt")?;
let reader = BufReader::new(file);
for line in reader.lines() {
println!("{}", line?);
}
Ok(())
}
This code opens the file "file.txt" using the File::open function and creates a BufReader object to read the file line by line. The lines function returns an iterator over the lines of the file, and we loop over each line and print it to the console. Note that the line? syntax is used to propagate any errors that might occur while reading the file.
3. Reading the contents of a file into a byte buffer:
use std::fs::File;
use std::io::{Read};
fn main() -> std::io::Result<()> {
let mut buffer = [0; 1024];
let mut file = File::open("file.txt")?;
// read up to 1024 bytes and return the number of bytes read
let bytes_read = file.read(&mut buffer)?;
// print the byte buffer as a string
println!("{}", String::from_utf8_lossy(&buffer[..bytes_read]));
Ok(())
}
This code reads up to 1024 bytes of the file "file.txt" into a byte buffer named buffer, using the Read trait's read method. The read method returns the number of bytes that were actually read, so we pass this value to from_utf8_lossy to convert the byte buffer to a string. Note that we are using a mutable reference to file and buffer, since we need to modify them to read data.